EDIT: Now I'm really confused. Sm4sh explorer used sdcafiine to add my mod automatically, it added 0 files, and it still doesn't work
The name for the songs are ok > snd_bng_{song_name}.nus3bank
if there's the folder ID corresponding to the region of your game at the root of your SD, it will use SDCafiine, if it's wiiu/games/{code of sm4sh for loadiine}, then it will load loadiine.
During the first export to SD, it will generate a few csv files, so it order to see what was seen and sent you can open them (cache/csv)
Also, I'll say it again, even though it's one of the first thing the program tells you, if you modify anything in the source folder in order to hack your way into extracting an existing mod, don't complain if you have issues in the future extracting anything. This is not supported and will not be supported.
If you absolutely want the mods, it's better to ask the creator to share the unpacked mod. As a last option, if you have the
packed file AND the resource file associated with it, you can extract it with dtlsextractor.
The resource file(s) tell the program where is what, without it you can't know what file is where. And with a wrong one the wrong information is given, resulting in many errors that some people have.
When you have a valid source (all the game file and patch) you can extract all the files (at least tested in US), except one in the spanish localization if I remember well.